Factors Influencing the Capacity Fade of Spinel Lithium Manganese Oxides

Abstract

With the aim of developing a better understanding of the capacity fading mechanisms of spinel manganese oxides, the percent capacity fade of a number of singly substituted LiMn 2Ϫy M y O 4 (M ϭ Li, Al, Ti, Co, Ni, and Cu and 0 р y р 0.2) and doubly substituted LiMn 2ϪyϪz M y Li z O 4 (M ϭ Al, Ti, Fe, Co, Ni, Cu, and Ga, 0 р y р 0.1, and 0 р z р 0.1) oxides is correlated to the initial lattice parameter, initial manganese valence, degree of manganese dissolution, electrode resistance, irreversible capacity ͑IRC͒ loss in the first cycle, and lattice parameter difference ⌬a between the two cubic phases formed in the two-phase region during the charge-discharge process. The doubly substituted LiMn 2ϪyϪz Ni y Li z O 4 samples exhibit a combination of superior capacity retention and rate capability with lower IRC compared to LiMn 2 O 4 despite a similar amount of manganese dissolution due to a low ⌬a and the consequent low microstrain. The samples with a low ⌬a are also characterized by a lower initial lattice parameter and a higher initial Mn valence of Ͼ3.58ϩ for the as-prepared samples. The percent capacity fade, IRC, and ⌬a all exhibit a sharp decrease as the initial Mn valence in the as-prepared sample exceeds 3.58ϩ.Lithium-ion batteries have become attractive for portable electronic devices. However, the high cost and toxicity of the currently used LiCoO 2 cathodes hinder the use of lithium-ion cells for electric vehicle applications. In this regard, the spinel LiMn 2 O 4 cathode has become appealing as Mn is inexpensive and environmentally benign, but it is plagued by severe capacity fade at elevated temperatures. Several mechanisms have been proposed over the years to account for the capacity fade. The mechanisms include ͑i͒ occurrence of lattice ͑Jahn-Teller͒ distortion on the surface of LiMn 2 O 4 due to inhomogeneity in discharge and formation of tetragonal Li 2 Mn 2 O 4 , 1 ͑ii͒ manganese dissolution into the electrolyte, 2,3 ͑iii͒ formation of oxygen defects, 4 ͑iv͒ formation of new phases, 5 ͑v͒ loss of crystallinity, 6,7 and ͑vi͒ instability arising from the existence of two cubic phases during the charge-discharge process. 8,9 Among the various mechanisms proposed, manganese dissolution is generally thought to be the most important factor. However, it has been suggested that the manganese dissolution could account for only some portion of the total capacity loss and that other factors may play a significant role. 3,8,10 Additionally, monitoring of the oxygen content of the chemically delithiated samples with lithium content has revealed that the Li 1Ϫx Mn 2 O 4 system does not lose any oxygen from the lattice, ruling out the role of formation of oxygen defects in the capacity fade. 11 We showed recently by investigating a series of singly substituted LiMn 2Ϫy M y O 4 (M ϭ Li, Al, Ti, Co, and Ni and 0 р y р 0.2) and doubly substituted LiMn 2ϪyϪz M y Li z O 4 (M ϭ Ti, Co, and Ni, 0 р y р 0.1, and 0 р z р 0.1) oxides that the samples that exhibit poor cyclability exhibit significant broadening of the diffr...

Cathode materials review

“…The 3D diffusion path in LiMn 2 O 4 provides excellent rate capability but suffers from severe capacity fading when cycling at elevated temperature. The reasons for this capacity fade were investigated, and two important mechanisms were proposed: 1) the dissolution of Mn 2+ in the electrolyte by the corrosion of H + ions and 2) the irreversible structural transformation from a spinel to a tetragonal structure due to the presence of Jahn-Teller (J-T) active Mn 3+ ions [38,39]. [42,43].…”

Effect of Electrochemical Charging on Elastoplastic Properties and Fracture Toughness of LiXCoO2

“…However, the electrode materials used in ion-intercalation batteries undergo significant composition changes-which correlate to high storage capacity-that can induce structural changes and mechanical stresses; these changes can degrade battery performance metrics such as power, achievable storage capacity, and lifetime. [1][2][3][4][5][6][7][8] Microstructural damage has been observed directly in numerous electrode materials subjected to electrochemical cycling, both within single crystals (or grains) and among polycrystalline aggregates. 4,5,[7][8][9][10][11][12][13][14][15] While the relationships among electrode microstructure, electrochemical cycling conditions, crystallographic changes in the active materials, and resulting mechanical stresses have been elucidated, relatively little is known about the composition-dependency of the key physical properties.…”

High Voltage Cathode Materials

“…The electrochemical reaction in Li x Ni y Mn 2−y O 4 has been described by several groups [2,17,45,46]. Using ultraviolet photoelectron spectroscopy, Gao et al [45] studied the top of the valence band of Li x Ni y Mn 2−y O 4 for a series of samples with 0.0 < y<0.5.…”